Field of the Invention
This invention relates generally to processing of solid materials, particularly fuel material solids such as carbonaceous fuel solids such as of granular form and, more specifically, to methods and devices for even distribution of such material solids over extended areas.
Discussion of Related Art
In recent years, such as due to concerns about global climate change, the atmospheric release of large quantities of CO2 in conjunction with power generation has come under close scrutiny, and new power sources have been sought which reduce CO2 emissions. A promising technology called oxy-combustion has been under development in many countries for more than a decade.
Such processing technology commonly employs a reactor consisting of a fluidized bed such as made up of an inert material or dolomite, or a combination of both. A solid carbonaceous, possibly sulfur-containing, fuel is injected into the reactor to be burned with oxygen or air. Recycled flue gas such as primarily composed of carbon dioxide and steam is used to fluidize the bed. CO2 may constitute 65-99% of the fluidizing gas for the bed, and steam may make up the remainder. Conventional oxy-combustion reactors premix all recycled flue gas with 20-30% or as much as 50% oxygen (molar percentage). This is a common generic recipe for oxy-combustion systems which have been proposed for optimized high carbon capture systems for producing power from coal, petroleum coke and biomass combustion.
In current, state of the art oxy-combustion technology such processing occurs at atmospheric pressure, and oxygen percentages above 50% and even as high as 100% have been performed which show no evidence of heat exchanger fouling, however at higher pressures above 3 or 4 atmospheres, the oxygen partial pressure can begin to cause ash particle melting, particle agglomeration and fouling.
A considerable amount of heat can be removed during flue gas water condensation if the process is carried out at high pressure, which allows more electrical power to be produced with high quality steam, and boiler feedwater can be preheated with the flue gas condensate. Therefore, a method of performing oxy-combustion at high pressure is highly desired to improve the system efficiency.
One implication of performing oxy-combustion in the conventional method described above but at high pressure is that the high oxygen content requires that carbonaceous fuel (such as coal, lignite, petroleum coke or biomass) be injected at a large particle diameter to prevent overheating, and consequently solids have to be circulated outside the bed via cyclones to ensure complete combustion (US 2014/0065559 A1).
Injecting pulverized coal into such a bed as described in patent application US 2010/0307389 A1 will allow complete combustion in a very short time, such that solids do not have to be circulated outside the bed, however this also has a risk that coal particles will burn faster than the heat can be removed and diffuse through the bed to heat transfer surfaces, and this can lead to fouling through slagging agglomeration. Moisture in the fuel has only a limited degree of mitigating effect, and using wet fuel has other detrimental effects on operating cost (more oxygen must be produced, and the solids cannot be handled in a conventional manner when they are not dried.)
In pressurized oxy-combustion, the problem of delivering the solid carbonaceous fuel (e.g., coal) and oxygen together requires that across a very large area of a fluidized bed, a large amount of coal will have to be distributed evenly.
One of the problems commonly associated with achieving desired fuel distribution in oxy-combustion processing is the inherent temperature of devolatization of the fuel. Each fuel will release hydrocarbons at elevated temperatures, and these tend to make the fuel sticky, and will rapidly plug pipes. The distribution method desirably must allow for fuel to be transported up to 20 or 30 feet across the diameter of a combustor without raising the temperature of the fuel up to devolatization temperatures.
Moreover, while distribution of the solid carbonaceous fuel (e.g., coal) across a very large area of a fluidized bed can be done relatively easily with existing designs if there is only one stage and fuel is delivered only to the bottom or the top of the bed, in a design for a compact pressurized fluidized bed combustor (PFBC) with finely pulverized coal, even distribution of the fuel must be done in successive stages, where existing manifold and distributor designs do not work. Coal must be distributed across a large surface with only 4.7-8.3 MWth/m2 (preferably about 6 MWth/m2). This requires about 2-4 injectors per square meter, coal feeders of about 1″ and orifices of about ¼ to ½ inch diameter. These feeders must be insulated from the combustion environment to prevent caking and plugging.
While other developments have been directed to specified designs for injecting coal and oxygen together, there remains a need for methods, devices and systems that permit and facilitate desired distribution of solid materials, particularly fuel material solids such as carbonaceous fuel solids such as of granular form, e.g., solid carbonaceous fuel, such as coal, via system features such as manifolds and hoppers, for example, to corresponding or associated injectors.